It is often desirable in today's technology to prevent precipitation of alkaline earth salts or of iron salts from water or aqueous solutions. For this purpose inorganic and organic sequestering agents have previously been proposed and utilized. For instance, the organic compounds nitrilo triacetic acid or ethylenediamine tetraacetic acid have been used. Likewise polymeric phosphates have also been used as sequestering agents. The latter have the advantage that they can prevent precipitation even if applied in less than a stoichiometric amount. The disadvantages of the polymeric phosphates, however, are that they lose effectiveness at elevated temperatures and that they readily hydrolyze, particularly in the acidic pH-range. For reasons related to sewage disposal, additional problems may develop in the use of phosphates. It has already been proposed to use organic phosphonic acids, such as non-substituted aminotrimethylene phosphonic acid, for this purpose, but it has been found that corrosion problems occur therefrom.